Double transition upshift control for an automatic transmission

ABSTRACT

An improved control method for properly coordinating a double transition upshift. The state changes of the various clutches of the transmission are sequenced in relation to a dynamic measure of the transmission speed ratio so as to provide consistent high quality shifting. Closed-loop pressure controls are employed in conjunction with the sequencing to ensure timely shift completion. &lt;IMAGE&gt;

This invention relates to upshift control of a multi-speed ratioautomatic transmission, and more particularly, to upshifts involvingmultiple stage control of the transmission friction elements.

BACKGROUND OF THE INVENTION

Automatic transmissions of the type addressed by this invention includeseveral fluid operated torque transmitting devices, referred to hereinas clutches, which are automatically engaged and disengaged according toa predefined pattern to establish different speed ratios between inputand output shafts of the transmission. The input shaft is coupled to aninternal combustion engine through a fluid coupling, such as a torqueconverter, and the output shaft is mechanically connected to drive oneor more vehicle wheels.

The various speed ratios of the transmission are typically defined interms of the ratio Ni/No, where Ni is the input shaft speed and No isthe output shaft speed. Speed ratios having a relatively high numericalvalue provide a relatively low output speed and are generally referredto as lower speed ratios; speed ratios having a relatively low numericalvalue provide a relatively high output speed and are generally referredto as upper speed ratios. Accordingly, shifts from a given speed ratioto a lower speed ratio are referred to as downshifts, while shifts froma given speed ratio to a higher speed ratio are referred to as upshifts.

Shifting from one speed ratio to another generally involves a transitionor state change of two clutches. That is, one clutch is engaged(on-coming) while another clutch is disengaged (off-going). The controlof this invention applies to a class of shifts involving two sets ofstate changes. These shifts are commonly referred to as doubletransition shifts. If the state changes involved in double transitionshifts are not properly coordinated, the speed ratio may initiallychange in an unintended direction or at an unintended rate, therebydegrading the shift quality.

SUMMARY OF THE PRESENT INVENTION

The present invention is directed to an improved control method forproperly coordinating a double transition upshift, wherein the statechanges of the various clutches are sequenced in relation to a dynamicmeasure of the transmission speed ratio so as to provide consistent highquality shifting. Closed-loop pressure controls are employed inconjunction with the sequencing to ensure timely shift completion.

A double transition downshift control, also disclosed herein, is thesubject of a co-pending patent application U.S. Ser. No. 07/651,870,filed 02/07/91, also assigned to the assignee of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1a-1b form a schematic diagram of a five-speed automatictransmission controlled in accordance with this invention by acomputer-based control unit.

FIG. 1c is a state diagram for the clutches of the transmission depictedin FIGS. 1a-1b.

FIG. 1d is a chart depicting the electrical state changes required forshifting from one speed ratio to another.

FIGS. 2 and 3 graphically depict double transition upshifting anddownshifting, respectively, for the transmission depicted in FIGS.1a-1b.

FIGS. 4, 5 and 6 depict flow diagrams representative of computer programinstructions executed by the control unit of FIG. 1a in carrying out theshift control of this invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIGS. 1a-1b of the drawings, the reference numeral 10generally designates a motor vehicle drivetrain including an engine 12and a planetary transmission 14 having a reverse speed ratio and fiveforward speed ratios. Engine 12 includes a throttle mechanism 16mechanically connected to an operator manipulated device, such as anaccelerator pedal (not shown), for regulating the air intake of theengine. The engine 12 is fueled by a conventional method in relation tothe air intake to produce output torque in proportion thereto. Suchtorque is applied to the transmission 14 through the engine output shaft18. The transmission 14, in turn, transmits engine output torque to anoutput shaft 20 through a torque converter 24 and one or more of thefluid operated clutches C1-C5, OC, Reverse clutch RC, and one-wayclutches 26-30, such clutches being applied or released according to apredetermined schedule for establishing a desired transmission speedratio.

Referring now more particularly to the transmission 14, the impeller orinput member 36 of the torque converter 24 is connected to be rotatablydriven by the output shaft 18 of engine 12 through the input shell 38.The turbine or output member 40 of the torque converter 24 is rotatablydriven by the impeller 36 by means of fluid transfer therebetween and isconnected to rotatably drive the turbine shaft 42. A stator member 44redirects the fluid which couples the impeller 36 to the turbine 40, thestator being connected through a one-way device 46 to the housing oftransmission 14.

The torque converter 24 also includes a clutch TCC comprising a clutchplate 50 secured to the turbine shaft 42. The clutch plate 50 has afriction surface 52 formed thereon adaptable to be engaged with theinner surface of the input shell 38 to form a direct mechanical drivebetween the engine output shaft 18 and the turbine shaft 42. The clutchplate 50 divides the space between input shell 38 and the turbine 40into two fluid chambers: an apply chamber 54 and a release chamber 56.

When the fluid pressure in the apply chamber 54 exceeds that in therelease chamber 56, the friction surface 52 of clutch plate 50 is movedinto engagement with the input shell 38, thereby engaging the TCC toprovide a mechanical drive connection in parallel with the torqueconverter 24. In such case, there is no slippage between the impeller 36and the turbine 40. When the fluid pressure in the release chamber 56exceeds that in the apply chamber 54, the friction surface 52 of theclutch plate 50 is moved out of engagement with the input shell 38 asshown in FIG. 1a, thereby uncoupling such mechanical drive connectionand permitting slippage between the impeller 36 and the turbine 40.

The turbine shaft 42 is connected as an input to the carrier Cf of aforward planetary gearset f. The sun Sf is connected to carrier Cf viathe parallel combination of one-way clutch F5 and friction clutch OC.The clutch C5 is selectively engageable to ground the sun Sf. The ringRf is connected as an input to the sun S1r of a compound rearwardplanetary gearset r via the parallel combination of one-way clutch F1and friction clutch C3. The clutch C2 selectively connects the forwardgearset ring Rf to rearward gearset ring Rr, and the Reverse clutch CR.selectively grounds the ring Rr. The sun S2r is selectively grounded byclutch C4 or by clutch C1 through the one-way clutch F2. The pinion Prmechanically couples the pinion gears and is connected as an output toshaft 20.

The various speed ratios and the clutch states required to establishthem are set forth in the chart of FIG. 1c. Referring to that Figure, itis seen that the Park/Neutral condition is established by releasing allof the clutches. A garage shift to Reverse is effected by engaging theC3, OC and RC clutches. In the forward speed ranges, a garage shift to1st is effected by engaging the clutches C1, C4 and OC. In this case,the forward gearset f is locked up and the one-way clutch F1 applies theturbine speed Nt as an input to the sun element Sr of rearward gearsetr, providing a Ni/No ratio of 3.61.

As the vehicle speed increases, an upshift from 1st to 2nd is effectedsimply by engaging clutch C2; the one-way clutch F1 overruns as soon ason-coming clutch C2 develops sufficient torque capacity. The forwardgearset f remains locked up, and the clutch C2 applies the turbine speedNt as an input to the ring element Rr of rearward gearset r to provide aNi/No ratio of 1.85. Downshifting from 2nd to 1st merely involvesreleasing clutch C2.

The upshift from 2nd to 3rd is effected by engaging clutch C5 andreleasing clutch OC so that the forward gearset operates as anoverdrive, thereby providing a Ni/No ratio of 1.37. Downshifting from3rd to 2nd is effected by releasing clutch C5 and engaging clutch OC toreturn the forward gearset f to a lock-up condition.

The upshift from 3rd and 4th is effected by releasing clutch C5 andengaging clutch OC to return the forward gearset f to a lock-upcondition, while releasing clutch C4 and engaging clutch C3 to lock-upthe rearward gearset r, one-way clutch F2 releasing the rear planet axisPr. In this case, the turbine speed Nt is transmitted directly to outputshaft 20 for a Ni/No ratio of 1.00. The downshift 4th to 3rd is effectedby releasing clutch OC and engaging clutch C5 to return the forwardgearset f to an overdrive condition, while releasing clutch C3 andengaging clutch C4 to apply the turbine speed Nt as an input to the ringelement Rr.

The timing of the 3-4 upshift and 4-3 downshift state changes must beproperly coordinated to avoid conditions which would cause the ratio tochange in the wrong direction or at the wrong rate. In the upshift, forexample, care must be taken to ensure that on-coming clutch C3 is readyto lock-up the rearward gearset r when off-going clutch C5 is releasedto lock-up the forward gearset f. Otherwise, the Ni/No ratio initiallyincreases from the 3rd ratio of 1.37 toward the 2nd ratio of 1.85.Conversely, in the 4-3 downshift, care must be taken to ensure thaton-coming clutch C5 is ready to engage to establish an overdrivecondition in the forward gearset f when off-going clutch C3 is released.Otherwise, the Ni/No ratio increases toward the 2nd ratio of 1.85instead of the 3rd ratio of 1.37. The control of this invention,described below, uses ratio feedback information to properly sequencethe clutch state changes for consistent high quality shifting.

Completing the shift analysis, the upshift from 4th to 5th is effectedby engaging clutch C5 and releasing clutch OC to operate the forwardgearset f in an underdrive condition, thereby providing a Ni/No ratio of0.74. Downshifting from 4th to 3rd is effected by releasing clutch C5and engaging clutch OC.

A positive displacement hydraulic pump 60 is mechanically driven by theengine output shaft 18. Pump 60 receives hydraulic fluid at low pressurefrom the fluid reservoir 64 and filter 65, and supplies line pressurefluid to the transmission control elements via output line 66. Apressure regulator valve (PRV) 68 is connected to the pump output line66 and serves to regulate the line pressure by returning a controlledportion of the line pressure to reservoir 64 via the line 70. The PRV 68is biased at one end by orificed line pressure in line 71 and at theother end by the combination of a spring force, a Reverse ratio fluidpressure in line 72 and a controlled bias pressure in line 74.

The Reverse fluid pressure is supplied by a Manual Valve 76, describedbelow. The controlled bias pressure is supplied by a Line Pressure BiasValve 78 which develops pressure in relation to the current supplied toelectric force motor 80. Line pressure is supplied as an input to valve78 via line 82, a pressure limiting valve 84 and filter 85. The limitedline pressure, referred to as ACT FEED pressure, is also supplied as aninput to other electrically operated actuators of the control system vialine 86. With the above-described valving arrangement, it will be seenthat the line pressure of the transmission is electrically regulated byforce motor 80.

In addition to regulating line pressure, the PRV 68 develops a regulatedconverter feed (CF) pressure for the torque converter 24 in line 88. TheCF pressure is supplied as an input to TCC Control Valve 90, which inturn directs the CF pressure to the release chamber 56 of torqueconverter 24 via line 92 when open converter operation is desired. Inthis case, the return fluid from torque converter 24 is exhausted vialine 94, the TCC Control Valve 90, an oil cooler 96 and an orifice 98.When closed converter operation is desired, the TCC Control Valve 90exhausts the release chamber 56 of torque converter 24 to an orificedexhaust 100, and supplies a regulated TCC apply pressure in line 102 tothe apply chamber 54, thereby engaging the TCC. The TCC apply pressurein line 102 is developed from line pressure by a TCC Regulator Valve104.

Both the TCC Control Valve 90 and the TCC Regulator Valve 104 are springbiased to effect the open converter condition, and in each case, thespring force is opposed by an electrically developed control pressure inline 106. The control pressure in line 106 is developed by the solenoidoperated TCC Bias Valve 108, through a ratiometric regulation of thefluid pressure in line 110. When closed converter operation is desired,the solenoid of TCC Bias Valve 108 is pulse-width-modulated at acontrolled duty cycle to ramp up the bias pressure in line 106. Biaspressures above the pressure required to shift the TCC Control Valve tothe closed-converter state are used to control the TCC apply pressuredeveloped in line 102 by TCC Regulator Valve 104. In this way, the TCCBias Valve 108 is used to control the torque capacity of the TCC whenclosed converter operation is desired.

The friction clutches C1-C5, OC and CR are activated by conventionalfluid operated pistons P1-P5, POC and PCR, respectively. The pistons inturn, are connected to a fluid supply system comprising the Manual Valve76 referred to above, the Shift Valves 120, 122 and 124, and theAccumulators 126, 128 and 130. The Manual Valve 76 develops supplypressures for Reverse (REV) and the various forward ranges (DR, D32) inresponse to driver positioning of the transmission range selector 77.The REV, DR and D32 pressures, in turn, are supplied via lines 72, 132and 134 to the various Shift Valves 120-124 for application to the fluidoperated pistons P1-P5, POC and PCR. The Shift Valves 120, 122 and 124are each spring biased against controlled bias pressures, the controlledbias pressures being developed by the solenoid operated valves A, C andB. The accumulators 126, 128 and 130 are used to cushion the apply, andin some cases the release, of clutches C5, C2 and C3, respectively.

A chart of the ON/OFF states of valves A, C and B for establishing thevarious transmission speed ratios is given in FIG. 1d. In Neutral andPark, the solenoids A, B and C are all off. In this condition, linepressure is supplied to clutch piston POC through orifice 176, but theremaining clutches are all disengaged. Reverse fluid pressure, whengenerated by Manual Valve 76 in response to driver displacement of rangeselector 77, is supplied directly to clutch piston P3 via lines 72, 73and 140, and to clutch piston PCR via lines 72, 142, orifice 144 andShift Valve 124.

A garage shift to the forward (Drive) ranges is effected when ManualValve 76 is moved to the D position, connecting line pressure to the DRpressure supply line 132. The DR pressure is supplied to the clutchpiston Pl via line 146 and orifice 148 to progressively engage clutchC1. At the same time, Solenoid Operated Valves A and C are energized toactuate Shift Valves 120 and 122. The Shift Valve 122 directs DRpressure in line 132 to clutch piston P4 via Regulator Valve 150 andline 152. The Shift Valve 120 supplies a bias pressure to the RegulatorValve 150 via line 154 to boost the C4 pressure. In this way, clutchesC1, C4 and OC are engaged to establish 1st speed ratio.

Referring to the chart of FIG. 1d, a 1-2 upshift is effected bydeenergizing Solenoid Operated Valve A to return Shift Valve 120 to itsdefault state. This routes DR pressure in line 132 to the clutch pistonP2 via Shift Valve 120, lines 156, 158 and 162, and orifice 160 toengage the clutch C2. Line 162 is also connected as an input toaccumulator 128, the backside of which is maintained at a regulatedpressure developed by valve 164. The engagement of clutch C2 is therebycushioned as the C2 apply pressure, resisted by spring force, strokesthe piston of accumulator 128. Of course, a 2-1 downshift is effected byenergizing the Solenoid Operated Valve A.

Referring again to the chart of FIG. 1d, a 2-3 upshift is effected byenergizing Solenoid Operated Valve B to actuate the Shift Valve 124.This exhausts the clutch piston POC via orifice 166 to release theclutch OC, and supplies line pressure in line 66 to clutch piston P5 viaorifice 168 and line 170 to progressively engage clutch P5. Line 170 isconnected via line 172 as an input to accumulator 126, the backside ofwhich is maintained at a regulated pressure developed by valve 164. Theengagement of clutch C5 is thereby cushioned as the C5 apply pressure,resisted by spring force, strokes the piston of accumulator 126. Ofcourse, a 3-2 downshift is effected by deenergizing the SolenoidOperated Valve B.

Referring again to the chart of FIG. 1d, a 3-4 upshift is effected bydeenergizing Solenoid Operated Valves B and C to return Shift Valves 124and 122 to their default positions, as depicted in FIGS. 1a-1b. TheShift Valve 124 thereby (1) exhausts clutch piston P5 and accumulator126 via line 170 and orifice 174 to release clutch C5, and (2) suppliespressure to clutch piston POC via lines 66 and 171 and orifice 176 toengage clutch OC. The Shift Valve 122 (1) exhausts clutch piston P4 vialine 152 and orifice 178 to release clutch C4, and (2) supplies DRpressure in line 132 to clutch piston P3 via Shift Valve 120, orifice180 and lines 182, 184, 73 and 140 to engage clutch C3. Line 182 isconnected via line 186 as an input to accumulator 130, the backside ofwhich is maintained at a regulated pressure developed by valve 164. Theengagement of clutch C3 is thereby cushioned as the C3 apply pressure,resisted by spring force, strokes the piston of accumulator 130. Ofcourse, a 4-3 downshift is effected by energizing the Solenoid OperatedValves B and C.

Referring again to the chart of FIG. 1d, a 4-5 upshift is effected byenergizing Solenoid Operated Valve B to actuate the Shift Valve 124.This exhausts the clutch piston POC via orifice 166 to release theclutch OC, and supplies line pressure in line 66 to clutch piston P5 viaorifice 168 and line 170 to progressively engage clutch P5. As indicatedbelow, line 170 is also connected via line 172 as an input toaccumulator 126, which cushions the engagement of clutch C5 as the C5apply pressure, resisted by spring force, strokes the piston ofaccumulator 126. Of course, a 5-4 downshift is effected by deenergizingthe Solenoid Operated Valve B.

The Solenoid Operated Valves A, B and C, the TCC Bias Valve 108 and theLine Pressure Bias Valve 78 are all controlled by a computer-basedTransmission Control Unit (TCU) 190 via lines 192-196. As indicatedabove, the valves A, B and C require simple on/off controls, while thevalves 108 and 78 are pulse-width-modulated (PWM). The control iscarried out in response to a number of input signals, including anengine throttle signal %T on line 197, a turbine speed signal Nt on line198 and an output speed signal No on line 199. The throttle signal isbased on the position of engine throttle 16, as sensed by transducer T;the turbine speed signal is based on the speed of turbine shaft 42, assensed by sensor 200; and the output speed signal is based on the speedof output shaft 20, as sensed by sensor 202. In carrying out thecontrol, the TCU 190 executes a series of computer program instructions,represented by the flow diagrams of FIGS. 4, 5 and 6 described below.

FIGS. 2 and 3 depict a 3-4 upshift and a 4-3 downshift, respectively,performed according to this invention. In the upshift of FIG. 2, Graph Adepicts the pressure supplied to off-going clutch C5, Graph B depictsthe ratio Ni/No, Graph C depicts the pressure supplied to on-comingclutch C3, and Graph D depicts the state of the Solenoid Operated ValvesB and C. In the downshift of FIG. 3, Graph A depicts the pressuresupplied to off-going clutch C3, Graph B depicts the ratio Ni/No, GraphC depicts the pressure supplied to on-coming clutch C5, and Graph Ddepicts the state of the Solenoid Operated Valves B and C.

Referring particularly to FIG. 2, and recalling the above discussion ofFIGS. 1a-1d, the 3-4 upshift is effected by deenergizing the SolenoidOperated Valve B to release clutch C5 while engaging clutch OC(locking-up the forward gearset f), and deenergizing the SolenoidOperated Valve C to release clutch C4 while engaging clutch C3,providing a direct or 1:1 ratio. Thus, the forward gearset f isincreasing in ratio (Ni/No) while the rearward gearset r is decreasingin ratio. This means that poor shift quality will result if the statechange of the forward gearset f occurs before the state change of therearward set. In practice, the critical elements are off-going clutch C5and on-coming clutch C3. If off-going clutch C5 is released beforeon-coming clutch C3 has achieved adequate torque capacity, the Ni/Noratio will increase instead of decrease.

The control of this invention addresses the above-mentioned timingconcerns by sequencing the deenergization of Solenoid Operated Valves Band C in response to a measure of the speed ratio Ni/No. The upshift isinitiated at time t0 by deenergizing the Solenoid Operated Valve C toinitiate engagement of clutch C3 while releasing clutch C4. This ineffect initiates a shift to the 5th ratio, as seen by the chart of FIG.1c. On-coming clutch C3 is filled in the interval t0-t1, whereafter theengagement pressure immediately jumps to an initial pressure Pi to beginengagement of the friction elements of clutch C3.

The increased clutch engagement pressure provides a corresponding torquecapacity, and the ratio Ni/No almost immediately begins to decrease, asseen in Graph B. The TCU 190 monitors the ratio, and initiatesdeenergization of the Solenoid Operated Valve B at time t2 when theratio decrease exceeds a threshold T3-4. This serves to releaseoff-going clutch C5 in the interval t2-t3, as seen in Graph A.Meanwhile, the C3 engagement pressure continues to increase along thesolid trace 204 as the piston of accumulator 130 is linearly displaced.When the accumulator 130 is fully stroked at time t4, the clutchengagement pressure rises substantially to line pressure Pline, as seenin Graph C.

An additional uncertainty in the 3-4 upshift concerns the torquecapacity of on-coming clutch C3 when off-going clutch C5 is fullyreleased at time t3. If the on-coming clutch torque capacity is too low,increased slippage will occur at the release of off-going clutch C5.This condition is manifested as a reduction in the rate of change ofratio, as indicated by the broken trace 206 of Graph B. According to oneaspect of this invention, the TCU 190 monitors the ratio Ni/No andreacts to the undercapacity condition by increasing the transmissionline pressure Pline by a specified percentage of its normal value. Thisproduces a corresponding and substantially immediate increase in thepressure applied to the back side of accumulator 130 via valve 164,which in turn, increases the on-coming clutch engagement pressure asindicated by the broken trace 208 in Graph C. The torque capacity ofclutch C3 experiences a similar increase, and the shift is completed atthe proper rate.

Referring particularly to FIG. 3, and recalling the above discussion ofFIGS. 1a-1d, the 4-3 downshift is effected by (1) energizing theSolenoid Operated Valve C to engage clutch C4 while releasing clutch C3,and (2) energizing the Solenoid Operated Valve B to engage clutch C5while releasing clutch OC. Here, the forward gearset f is decreasing inratio (direct to overdrive) while the rearward gearset r is increasingin ratio (direct to underdrive). This means that poor shift quality willresult if the state change of the forward gearset f occurs before thestate change of the rearward gearset r. Again, the critical elements areon-coming clutch C5 and off-going clutch C3. If off-going clutch C3 isreleased before on-coming clutch C5 has achieved adequate torquecapacity, a shift to the 2nd speed ratio will be initiated.

As in the upshift of FIG. 2, the downshift timing concerns are addressedby sequencing the energization of Solenoid Operated Valves B and C inresponse to a measure of the speed ratio Ni/No. The upshift is initiatedat time t0 by energizing the Solenoid Operated Valve B to initiateengagement of on-coming clutch C5 while releasing clutch OC. This ineffect initiates a shift to the 5th ratio, as seen by the chart of FIG.1c. On-coming clutch C5 is filled in the interval t0-t1, whereafter theengagement pressure immediately jumps to an initial pressure Pi to beginengagement of the friction elements of clutch C5.

The increased clutch engagement pressure provides a corresponding torquecapacity, and the ratio Ni/No almost immediately begins to decrease, asindicated by the solid trace 210 in Graph B. The TCU 190 monitors theratio, and initiates energization of the Solenoid Operated Valve C attime t2 when the ratio decrease exceeds a threshold T4-3. This serves torelease off-going clutch C3 in the interval t2-t3, as seen in Graph A.Meanwhile, the C5 engagement pressure continues to increase along thesolid trace 212 as the piston of accumulator 126 is linearly displaced.When the accumulator 126 is fully stroked at time t4, the clutchengagement pressure rises substantially to line pressure Pline, as seenin Graph C.

The above-described control ensures that the on-coming clutch C5 hasstarted to engage before the off-going clutch C3 is released. However,the threshold T4-3 must be very small so that the initial decrease inratio in the interval t1-t2 is not perceptible to the occupants of thevehicle. Accordingly, there is little information as to the magnitude ofthe on-coming torque capacity. If the on-coming torque capacity is toohigh, as indicated by the broken trace 214 in Graph C, the ratio willdecrease at a relatively high rate, as indicated by the broken trace 216in Graph B. If this occurs, the amount by which the ratio decreasesprior to the release of off-going clutch C3 will significantly exceedthe threshold T4-3, significantly degrading the shift quality. On theother hand, if the on-coming torque capacity is too low, as indicated bythe broken trace 218 in Graph C, the ratio will increase at a relativelyhigh rate, as indicated by the broken trace 220 in Graph B, exceedingthe 3rd speed ratio of 1.37. This effect is manifested as engine flare,and also significantly degrades the shift quality.

The TCU 190 monitors the ratio Ni/No and reacts to the under orovercapacity condition of the on-coming clutch by adaptively increasingthe transmission line pressure Pline by a predetermined amount in thepresent and subsequent 4-3 downshifts. An overcapacity condition isindicated if the ratio falls below an overcapacity adaptive thresholdRad(o); in this case, the line pressure Pline is reduced by apredetermined amount, 43 MOD. An undercapacity condition is indicated ifthe ratio exceeds an undercapacity adaptive threshold Rad(u); in thiscase, the line pressure Pline is increased by the amount 43 MOD. As withthe upshift, the increased or decreased line pressure results in acorresponding increase in the pressure applied to the back side ofaccumulator 126 via valve 164, which in turn, produces increased ordecreased on-coming clutch engagement pressure. In subsequent 4-3downshifts, the on-coming torque capacity will more closely approximatethe ideal value, and shift quality will be improved.

Referring now to FIGS. 4-5, the flow diagram of FIG. 4 represents a mainor executive computer program which is periodically executed in thecourse of vehicle operation in carrying out the control of thisinvention. The block 230 designates a series of program instructionsexecuted at the initiation of each period of vehicle operation forsetting various terms and timer values to an initial condition.Thereafter, the blocks 232-238 are executed to read the various inputsreferenced in FIG. 1a and to determine the desired speed ratio Rdes andthe torque converter clutch duty cycle TCC(DC). The desired ratio Rdesmay be determined in a conventional manner as a predefined function ofengine throttle position %T and output speed No. The torque converterclutch duty cycle TCC(DC) may be determined as a function of thethrottle position, output speed No and the difference between input andoutput speeds Ni and No.

If the actual ratio Ract--that is, Ni/No--is equal to the desired ratioRdes, as determined at block 238, the block 244 is executed to determinethe desired line pressure LPdes. In this case, the desired line pressureLPdes is determined as a function of throttle position and output speed,and also is adjusted based on the desired ratio Rdes and an adaptivecorrection term Pad. The adaptive correction term Pad may be generatedduring upshifting, based on shift time, as set forth in the U.S. Pat.No. 4,283,970 to Vukovich et al., issued Aug. 18, 1981, and assigned tothe assignee of this invention.

If an upshift is required, as determined by blocks 238 and 240, theblocks 242 and 244 are executed to perform the Upshift Logic of FIG. 5in addition to determining the desired line pressure LPdes, as describedabove. If a downshift is required, as determined by blocks 238 and 240,the blocks 246 and 248 are executed to perform the Downshift Logic ofFIG. 6 and to determine the desired line pressure LPdes. Here, thedesired line pressure is determined as a function of throttle positionand output speed, but is adjusted based on the pre-shift, or old ratioRold, the adaptive correction term Pad, and a further adaptivecorrection term P43ad if the shift is a 4-3 downshift. In any case, theblock 250 is then executed to convert the desired line pressure LPdes toa solenoid duty cycle LP(DC) and to output the various duty cycles anddiscrete solenoid states to the solenoid operated valves described abovein reference to FIGS. 1a-1b.

Referring now to the Upshift Logic of FIG. 5, the decision block 260 isfirst executed to determine if the shift is a 3-4 upshift; that is, adouble transition upshift. If not, the solenoid states A, B and C aresimply set in accordance with the chart of FIG. 1d, completing theroutine, as indicated by the block 262. If the shift is a 3-4 upshift,the block 264 is immediately executed to deenergize solenoid C. Thisinitiates the filling of on-coming clutch C3, as described above inreference to FIG. 2. Once the consequent decrease in ratio Ni/No exceedsthe threshold T3-4, as determined at block 266, the block 268 isexecuted to deenergize solenoid B, initiating the release of theoff-going clutch C5.

Decision block 270 then determines if the BOOST flag is set; initially,it is cleared by the initialization block 230. If not set, the blocks272-276 are executed to boost the desired line pressure LPdes upondetection of a predefined reduction in the rate of change of speedratio. The block 272 stores the current value of the change in ratio,dRAT, in the term dRAT(OLD), and determines the new change of ratio dRATaccording to the difference [RAT(LAST)-RAT], where RAT is the currentmeasure of the speed ratio Ni/No and RAT(LAST) is the previous measureof the speed ratio. The block 274 then determines if the rate of changein ratio, that is [dRAT(OLD)-dRAT], exceeds the reference value K. Thiscorresponds to a change in the slope of the trace depicted in Graph B ofFIG. 2, as described above. If the condition is met, on-coming clutch C3does not have sufficient torque capacity, and the block 276 is executedto set the BOOST flag and to increase the desired line pressure LPdes bya specified amount such as 10% of its normal value. This corresponds tothe broken trace 208 in Graph C of FIG. 2.

Referring now to the Downshift Logic of FIG. 6, the decision block 260is first executed to determine if the shift is a 4-3 downshift; that is,a double transition downshift. If not, the solenoid states A, B and Care simply set in accordance with the chart of FIG. 1d, completing theroutine, as indicated by the block 282. If the shift is a 4-3 downshift,the block 284 is immediately executed to energize solenoid B. Thisinitiates the filling of on-coming clutch C5, as described above inreference to FIG. 3. Once the consequent decrease in ratio (1.00-RAT)exceeds the threshold T4-3, as determined at block 286, the block 288 isexecuted to energize solenoid C, initiating the release of off-goingclutch C3.

The block 290 is then executed to determine if the entry conditions foradaptive adjustment of the transmission line pressure are satisfied. Theentry conditions ensure that adaptive pressure corrections are only madeif the shift is a normal 4-3 downshift. For example, the transmissionoil temperature must be within a normal operating range, the enginethrottle position must not change by more than a certain amount duringthe shift, and an adaptive correction must not have already been madebased on the current downshift. Assuming the entry conditions are met,the block 292 is executed to determine if the speed ratio RAT is greaterthan the undercapacity adaptive ratio threshold Rad(u). If so, thetorque capacity of on-coming clutch C5 is too low, and the block 294 isexecuted to set the adaptive pressure modifier term P43MOD to +K. Asindicated at block 296, the adaptive pressure modifier term P43MOD isthen added to the cumulative 4-3 adaptive term P43ad, which in turn, isfactored into the desired line pressure term LPdes at block 248 of FIG.4.

If block 292 is answered in the negative, the block 298 is executed todetermine if the speed ratio RAT is less than the overcapacity adaptiveratio threshold Rad(o). If so, the torque capacity of on-coming clutchC5 is too high, and the block 300 is executed to set the adaptivepressure modifier term P43MOD to -K. As indicated above, the block 296then adds the adaptive pressure modifier term P43MOD to the cumulative4-3 adaptive term P43ad. In either event, the adaptive pressurecorrection will have little effect in the current shift. In subsequent4-3 downshifts, however, the line pressure will be incrementallymodified so that the observed change in ratio will more nearlyapproximate the solid trace of Graph B, FIG. 3. If the entry conditionsare not met, or once an adaptive pressure correction has been made asdescribed above, the block 290 will be answered in the negative, andexecution of the blocks 292-300 will be skipped as indicated by flowdiagram line 302.

While this invention has been described in reference to the illustratedembodiment, it is expected that various modifications will occur tothose skilled in the art. In this regard, it should be realized thatcontrols incorporating such modifications may fall within the scope ofthis invention, which is defined by the appended claims.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. In an automatictransmission including input and output shafts coupled through first andsecond interconnected gearsets, each gearset being adapted to providemultiple speed ratios, and various selectively engageable torquetransmitting devices adapted to change speed ratios provided by saidfirst and second gearsets to thereby establish multiple overall speedratios between said input and output shafts, an upshift being carriedout by releasing an off-going torque transmitting device to increase thespeed ratio provided by said first gearset while applying an on-comingtorque transmitting device to decrease the speed ratio provided by saidsecond gearset, thereby achieving a decrease in the overall speed ratiobetween said input and output shafts, a method of operation forcoordinating such release and apply, comprising the steps of:initiatingthe apply of said on-coming torque transmitting device at a predefinedrate to effect an initial decrease in said overall speed ratio;initiating the release of said off-going torque transmitting device whena specified decrease in the overall speed ratio is detected; detecting acondition of insufficient torque capacity of said on-coming torquetransmitting device based on a determined rate of change of said overallspeed ratio during the release of said off-going torque transmittingdevice; and increasing the rate of apply of said on-coming torquetransmitting device in response to such detection to thereby achieve atimely completion of said upshift.
 2. The method set forth in claim 1,wherein the step of detecting a condition of insufficient torquecapacity of said on-coming torque transmitting device includes the stepsof:periodically measuring the overall speed ratio; periodicallycomputing a ratio rate based upon a difference between such measuredoverall speed ratio and a previous measure of said overall speed ratio;comparing such computed ratio rate with a previously computed ratio rateto detect a specified difference therebetween indicative of asubstantial reduction in the rate of change of said overall speed ratio.3. The method set forth in claim 1, wherein the on-coming torquetransmitting device develops torque capacity in relation to the fluidpressure supplied thereto, and the step of increasing the rate of applyof said on-coming torque transmitting device is carried out byincreasing the fluid pressure supplied to such on-coming torquetransmitting device.